There have been demands for a greater amount of displacement achieved in a multi-layer piezoelectric element under a high pressure as well as size reduction. As a result, the multi-layer piezoelectric element is required to be operable under harsher conditions, namely continuous operation over a long period of time with higher voltage applied thereto.
Unlike other multi-layer electronic components such as capacitor, the multi-layer piezoelectric element itself undergoes continuous changes in dimension during operation. A large amount of displacement of the multi-layer piezoelectric element as a whole is achieved as all piezoelectric material layers act while maintaining firm contact with each other with internal electrodes interposed therebetween. As a result, the element is subject to intense stresses.
As a solution to the problem described above, such an element has been proposed as a porous layer is provided as a target fracture layer in the inside of the piezoelectric material layer (Patent Document 1). Patent document 1 describes an attempt to mitigate the stress generated in each of the piezoelectric material layers by causing the multi-layer piezoelectric element to break in the target fracture layer. Such a multi-layer piezoelectric element has also been proposed that has target fracture layer in the inside of the internal electrode, rather than in the piezoelectric material layer.    Patent Document 1: Kohyo (National Publication of Translated Version) No. 2006-518934